The present invention generally relates to wireless communication networks, and particularly relates to power control in such networks.
Wireless communication networks typically employ some form of closed-loop power control for the communication signals going between base stations and the mobile stations being supported by those base stations. In particular, the typical Code Division Multiple Access (CDMA) network uses forward and reverse link power controls to control transmission powers by base stations on the forward link and by mobile stations on the reverse link. For example, network base stations must receive signals on the reverse link from mobile stations at signal strengths sufficient to permit data reception at tolerable error rates. However, to reduce each mobile station's contribution to overall reverse link interference, the network controls each mobile station such that it on average transmits at no higher power than is required to achieve the targeted received signal strength at one or more network base stations.
In a typical approach, the network employs both “inner” and “outer” loop reverse link power control. Inner loop power control involves relatively fast, ongoing power control adjustments of the mobile station's reverse link transmit power by the network. For example, in CDMA networks configured according to IS-2000 standards, inner loop control is based on the network streaming power control commands to the mobile station at up to 800 Hz, i.e., one power control command every 1.25 ms.
In response to each received command, the mobile station adjusts its pilot signal power upward or downward by a defined incremental step, depending on whether the received command was an up or a down command. A given base station supporting the mobile station determines whether to send an up or a down command based on the signal strength of the mobile station's signal as received at the base station. In particular, the typical base station monitors the received signal strength of the mobile station's pilot signal relative to a target value and sends an up command if the received signal strength is below the target, or sends a down command if the received signal strength is above the target. Because the typical mobile station is configured to transmit all of its reverse link signals, e.g., traffic channel and/or control channel signals, at defined ratios of pilot signal power, the up and down commands from the network cause the mobile station to increase and decrease, respectively, the power, of all its reverse link signal transmissions.
Outer loop reverse link power control runs at a slower rate and involves adjusting the inner loop signal strength target at the base station up or down based on some other reception parameter. Commonly the Frame Error Rate (FER) of the mobile station's traffic channel signal provides the metric for adjusting the inner loop target. For example, if the FER is low compared to a 1% (or other) target error rate, the base station may adjust the inner loop target downward. Conversely, if the FER exceeds the target error rate, the base station may adjust the inner loop target upward. In this manner, the base station's inner loop provides rapid closed-loop control of the mobile station's transmit power to maintain the as-received signal strength of the mobile station's pilot signal at or around a target value, while outer loop control provides a slower adjustment mechanism to ensure that the target value yields tolerable data error rates.
For certain types of forward link channels, e.g., dedicated traffic channels, similar inner and outer loop control mechanisms are embodied at the mobile stations. Thus, a given mobile station streams up/down power control commands to the network based on whether it receives a particular signal, e.g., a traffic channel signal, from the network at a signal strength above or below a target value. Further, the mobile station adjusts the target value up or down based on, for example, a FER of data received on the traffic channel signal.